Diffusive over-hydration of olivine-hosted melt inclusions

The pre-eruptive water content of magma is often estimated using crystal-hosted melt inclusions. However, olivine-hosted melt inclusions are prone to post-entrapment modification by H+ diffusion as they re-equilibrate with their external environment. This effect is well established for the case of H+ loss from olivine-hosted inclusions that have cooled slowly in degassed magma. Here we present evidence for the opposite effect: the addition of H+ into inclusions that are held in melts that are enriched in H2O with respect to the trapped melts. The compositional variability in a suite of 211 olivine-hosted inclusions from the Laki and Skuggafjöll eruptions in Iceland's Eastern Volcanic Zone indicates that diffusive H+ gain governs the H2O content of incompatible trace element depleted inclusions. Individual eruptive units contain olivine-hosted inclusions with widely varying incompatible element concentrations but near-constant H2O. Furthermore, over 40% of the inclusions have H2O/Ce>380H2O/Ce>380, significantly higher than the H2O/Ce expected in primary Icelandic melts or mid-ocean ridge basalts (150–280). The fact that the highest H2O/Ce ratios are found in the most incompatible element depleted inclusions indicates that hydration is a consequence of the concurrent mixing and crystallisation of compositionally diverse primary melts. Hydration occurs when olivines containing depleted inclusions with low H2O contents are juxtaposed against more hydrous melts during mixing. Melt inclusions from a single eruption may preserve evidence of both diffusive H+ loss and H+ gain. Trace element data are therefore vital for determining H2O contents of melt inclusions at the time of inclusion trapping and, ultimately, the H2O content of the mantle source regions.This work was supported by NERC grant NE/I012508/1 and a NERC studentship NE/1528277/1 to DAN. MEH acknowledges a Junior Research Fellowship from Murray Edwards College, Cambridge.This is the final published version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0012821X15003647#

On the flow of non-axisymmetric perturbations of cylinders via surface diffusion

We study the surface diffusion flow acting on a class of general (non--axisymmetric) perturbations of cylinders $\mathcal{C}_r$ in ${\rm I \! R}^3$. Using tools from parabolic theory on uniformly regular manifolds, and maximal regularity, we establish existence and uniqueness of solutions to surface diffusion flow starting from (spatially--unbounded) surfaces defined over $\mathcal{C}_r$ via scalar height functions which are uniformly bounded away from the central cylindrical axis. Additionally, we show that $\mathcal{C}_r$ is normally stable with respect to $2 \pi$--axially--periodic perturbations if the radius $r > 1$,and unstable if $0 < r < 1$. Stability is also shown to hold in settings with axial Neumann boundary conditions.Comment: 20 pages, 1 figure, submitted for publicatio

Use of Optical Genome Mapping to Detect Structural Variants in Neuroblastoma

\ua9 2023 by the authors.Background: Neuroblastoma is the most common extracranial solid tumour in children, accounting for 15% of paediatric cancer deaths. Multiple genetic abnormalities have been identified as prognostically significant in neuroblastoma patients. Optical genome mapping (OGM) is a novel cytogenetic technique used to detect structural variants, which has not previously been tested in neuroblastoma. We used OGM to identify copy number and structural variants (SVs) in neuroblastoma which may have been missed by standard cytogenetic techniques. Methods: Five neuroblastoma cell lines (SH-SY5Y, NBLW, GI-ME-N, NB1691 and SK-N-BE2(C)) and two neuroblastoma tumours were analysed using OGM with the Bionano Saphyr\uae instrument. The results were analysed using Bionano Access software and compared to previous genetic analyses including G-band karyotyping, FISH (fluorescent in situ hybridisation), single-nucleotide polymorphism (SNP) array and RNA fusion panels for cell lines, and SNP arrays and whole genome sequencing (WGS) for tumours. Results: OGM detected copy number abnormalities found using previous methods and provided estimates for absolute copy numbers of amplified genes. OGM identified novel SVs, including fusion genes in two cell lines of potential clinical significance. Conclusions: OGM can reliably detect clinically significant structural and copy number variations in a single test. OGM may prove to be more time- and cost-effective than current standard cytogenetic techniques for neuroblastoma

Trypanosoma brucei BRCA2 acts in a life cycle-specific genome stability process and dictates BRC repeat number-dependent RAD51 subnuclear dynamics

Trypanosoma brucei survives in mammals through antigenic variation, which is driven by RAD51-directed homologous recombination of Variant Surface Glycoproteins (VSG) genes, most of which reside in a subtelomeric repository of &gt;1000 silent genes. A key regulator of RAD51 is BRCA2, which in T. brucei contains a dramatic expansion of a motif that mediates interaction with RAD51, termed the BRC repeats. BRCA2 mutants were made in both tsetse fly-derived and mammal-derived T. brucei, and we show that BRCA2 loss has less impact on the health of the former. In addition, we find that genome instability, a hallmark of BRCA2 loss in other organisms, is only seen in mammal-derived T. brucei. By generating cells expressing BRCA2 variants with altered BRC repeat numbers, we show that the BRC repeat expansion is crucial for RAD51 subnuclear dynamics after DNA damage. Finally, we document surprisingly limited co-localization of BRCA2 and RAD51 in the T. brucei nucleus, and we show that BRCA2 mutants display aberrant cell division, revealing a function distinct from BRC-mediated RAD51 interaction. We propose that BRCA2 acts to maintain the huge VSG repository of T. brucei, and this function has necessitated the evolution of extensive RAD51 interaction via the BRC repeats, allowing re-localization of the recombinase to general genome damage when needed

Volatile and light lithophile elements in high-anorthite plagioclase-hosted melt inclusions from Iceland

Melt inclusions formed during the early stages of magmatic evolution trap primitive melt compositions and enable the volatile contents of primary melts and the mantle to be estimated. However, the syn- and post-entrapment behaviour of volatiles in primitive high-anorthite plagioclase-hosted melt inclusions from oceanic basalts remains poorly constrained. To address this deficit, we present volatile and light lithophile element analyses from a well-characterised suite of nine matrix glasses and 102 melt inclusions from the 10 ka Grímsvötn tephra series (i.e., Saksunarvatn ash) of Iceland’s Eastern Volcanic Zone (EVZ). High matrix glass H$_{2}$O and S contents indicate that eruption-related exsolution was arrested by quenching in a phreatomagmatic setting; Li, B, F and Cl did not exsolve during eruption. The almost uniformly low CO$_{2}$ content of plagioclase-hosted melt inclusions cannot be explained by either shallow entrapment or the sequestration of CO$_{2}$ into shrinkage bubbles, suggesting that inclusion CO$_{2}$ contents were controlled by decrepitation instead. High H$_{2}$O/Ce values in primitive plagioclase-hosted inclusions (182–823) generally exceed values expected for EVZ primary melts ($\sim$180), and can be accounted for by diffusive H2O gain following the entrainment of primitive macrocrysts into evolved and H$_{2}$O-rich melts a few days before eruption. A strong positive correlation between H$_{2}$O and Li in plagioclase-hosted inclusions suggests that diffusive Li gain may also have occurred. Extreme F enrichments in primitive plagioclase-hosted inclusions (F/Nd = 51–216 versus $\sim$15 in matrix glasses) possibly reflect the entrapment of inclusions from high-Al/(Al + Si) melt pools formed by dissolution-crystallisation processes (as indicated by HFSE depletions in some inclusions), and into which F was concentrated by uphill diffusion since F is highly soluble in Al-rich melts. The high S/Dy of primitive inclusions ($\sim$300) indicates that primary melts were S-rich in comparison with most oceanic basalts. Cl and B are unfractionated from similarly compatible trace elements, and preserve records of primary melt heterogeneity. Although primitive plagioclase-hosted melt inclusions from the 10 ka Grímsvötn tephra series record few primary signals in their volatile contents, they nevertheless record information about crustal magma processing that is not captured in olivine-hosted melt inclusions suites.D.A.N. acknowledges support from the Natural Environment Research Council (NE/1528277/1) and the Alexander von Humboldt Foundation. SIMS analyses were supported by a Natural Environment Research Council Ion Microprobe Facility award (IMF508/1013)

Intracluster gas pressure, entropy injection and redshift evolution

We study the effect of entropy injection in the intracluster medium (ICM) in light of the recent observationally determined universal pressure profile of the ICM. Beginning with a power-law entropy profile that is expected in the absence of any feedback, we show that a simple universal prescription of entropy injection results in the final, observed universal pressure profile. This simple prescription has two components, one associated with an overall increase in entropy and another associated with injection in the central parts of the cluster. Importantly, both the components of entropy injection are needed to produce the final universal pressure profile. This is indicative of a need of both preheating the ICM as well {\it in situ} AGN/SNe heating. We demonstrate the usefulness of the method by extending the calculations to clusters at high redshift, and predict redshift evolution of cluster scaling relations that can be tested against data. We show that the self-similar evolution of the universal pressure profile is equivalent to a negative evolution of entropy injection with redshift, with a scaling $S_{inj} \propto (1+z)^{-0.8} S_{inj}(z=0)$. We also show the current observational data are indicative of the entropy injection decreasing with redshift.Comment: 9 pages, 8 figures, accepted for publication in MNRAS, Comments welcom

Sunyaev-Zel'dovich clusters in millennium gas simulations

Large surveys using the Sunyaev–Zel’dovich (SZ) effect to find clusters of galaxies are now starting to yield large numbers of systems out to high redshift, many of which are new dis- coveries. In order to provide theoretical interpretation for the release of the full SZ cluster samples over the next few years, we have exploited the large-volume Millennium gas cosmo- logical N-body hydrodynamics simulations to study the SZ cluster population at low and high redshift, for three models with varying gas physics. We confirm previous results using smaller samplesthattheintrinsic(spherical)Y500–M500relationhasverylittlescatter(σlog10Y ≃0.04), is insensitive to cluster gas physics and evolves to redshift 1 in accordance with self-similar expectations. Our preheating and feedback models predict scaling relations that are in excel- lent agreement with the recent analysis from combined Planck and XMM–Newton data by the Planck Collaboration. This agreement is largely preserved when r500 and M500 are derived using thehydrostaticmassproxy,YX,500,albeitwithsignificantlyreducedscatter(σlog10Y ≃0.02),a result that is due to the tight correlation between Y500 and YX,500. Interestingly, this assumption also hides any bias in the relation due to dynamical activity. We also assess the importance of projection effects from large-scale structure along the line of sight, by extracting cluster Y500 values from 50 simulated 5 × 5-deg2 sky maps. Once the (model-dependent) mean signal is subtracted from the maps we find that the integrated SZ signal is unbiased with respect to the underlying clusters, although the scatter in the (cylindrical) Y500–M500 relation increases in the preheating case, where a significant amount of energy was injected into the intergalactic medium at high redshift. Finally, we study the hot gas pressure profiles to investigate the origin of the SZ signal and find that the largest contribution comes from radii close to r500 in all cases. The profiles themselves are well described by generalized Navarro, Frenk & White profiles but there is significant cluster-to-cluster scatter. In conclusion, our results support the notion that Y500 is a robust mass proxy for use in cosmological analyses with clusters